Vacuum tube device



Jan. 28, 1941. R SCHARFNAGEL 2,229,772

VACUUM TUBE DEVICE Filed F'eb. 21, '1939 fnl/enfan- Rudoy @way/7gg?! by Patented Jan. 28, 1941 UNITED STATES PATENT OFFCE VACUUIVI TUBE DEVICE Application February 21, 1939, Serial No. 257,591 In Germany February 25, 1938 2 Claims.

This invention relates to vacuum tube devices, and more particularly to electron discharge devices having a metallic envelope.

It is a well known expedient in connection with 5 electron discharge devices lto make the envelope of a metallic material in order to ensure sumcient stability with respect to mechanical stresses and adequate heat conduction from such devices during their operation.

'Ihe metallic materials or metals constituting such an envelope must satisfy a variety of requirements. Such metals must in the rst instance be capable of being intimately united with an insulating fusible melt, such as glass, so as to form a perfect vacuum seal either when jointed to a member of insulation, such as a ceramic substance, or when the vitreous melt serves as protective insulation for lead-in conductors be 2o ing carried through the metallic envelope. On

^ the other hand, the metals themselves must be perfectly vacuum-tight and of such nature that Vno gases are produced therein when heated to high temperaturesduring the operation of the electron discharge device. These requirements are particularly dicult to satisfy when the necessary sealing operations are made by means of materials having a very high melting point. However, such refractory materials are preferred in order to obviate injuries to the sealed joints 0 or points, even at the highest operating temperatures.

It is well known to employ the metallic envelope of an electronic discharge devi-ce as an electrode of the device in order to provide direct 35l heat conduction to the surrounding medium.

Experience has shown that a discharge tube envelope made of a pure metal, such as iron, sho-ws a certain tendency of oxidation at its inner surfaces not only on account of the high tem- 401 perature to which the envelope becomes heated when the lead-in conductors are sealed in their proper positions and when residual gases are removed by means of a high vacuum pump, but also during the actual high temperature opera 45, tion of the tube. This phenomenon which is due to the formation of oxidic layers on the inner surface of the envelope gives rise to the formation of gas during operation which considerably affects the properties of the electronic discharge 502 device in a deleterious sense.

The above mentioned and other disadvantages occurring in connection with electron discharge devices having a metallic envelope preferably bforming part of the electrode system of such 551 devices are reliably eliminated according to the main feature of my present invention which proposes the use of a non-oxidizing steel as the material of which the envelope consists. Inves- (Cl. Z50-27.5)

tigations have proven that a steel material composed of .8 per cent carbon with an additional amount of molybdenum and chromium of approximately 10 per cent is particularly well adapted for the manufacturing of envelopes for electron discharge devices. A tube envelope of a material with the above stated composition involves the essential advantage that its surface remains unaffected during operation, while on 10 the other hand this material is easily and reliably fusible with glass.

The accompanying drawing shows one embodiment of an electron discharge device to which the above identied invention has been applied. 15 The discharge device thus shown has a cylindrical member I of a steel material of the above mentioned composition and this member simultaneously acts as envelope of the device and as anode of the electrode system thereof. One end of the member I is closed by a cover 2 of a 20 ceramic substance and the joint between the member I and the cover 2 is coated by a vitreous melt 3. The other electrodes, that is, a grid 4 and a cathode 5, are sealed in the said cover 2 and the seals thus obtained are likewise coated 25 by the vitreous melt 3. The end of the cylinder I remote from the cover 2 is provided with a cap 6 of glass sealed, thereto. This cap carries in its inner portion the getter material supporting means and forms the pipe by means of which the tube is connected to the vacuum pump. This pipe (not shown) is removed by sealing at the end of the evacuation.

What is claimed is:

1. A vacuum tube device comprising, a metallic envelope, closing means therefor, an electrode system partially formed by said metallic envelope and partially by individual electrodes sealed in either of said closing means and extending into said tube device, the said metallic envelope being made of steel which contains .8 per cent carbon and an additional amount of molybdenum and lchromium of substantially 10 per cent.

l2. A vacuum tube device comprising, a cylindrical metallic envelope, a closing member of a ceramic material at one end of said envelope, a cap-shaped member of glass closing the other end of said envelope and carrying the getter material supporting means, an electrode system partially formed by said cylindrical metallic envelope and partially by individual electrodes sealed in said closing member and extending into said tube device, the said metallic envelope being made of steel which contains .8 per cent carbon and an additional amount of molybdenum and chromium of substantially 10 per cent.

RUD. SCHARFNAGEL. 

